Many mobile phones, PDAs, computers (laptop, monitor) etc., are equipped with a camera in front of the device, usually intended for video calls, in which the image of the user is transmitted to a receiving party.
The camera is usually placed on a top or bottom portion of the phone house or upper edge of the computer display and may define the size/length of this part of the device. Thus, when the user makes a video call, the user does not look the other party in the eye as his/her focus is on the screen looking at the other party.
This makes the video calls less attractive and may annoy the user when he/she changes focus between the camera and screen content.